Intravenous infusion and removal of fluid from a person's body using a catheter have been widely practiced for many years. A venous catheter is a tubular member having a needle at its working end. The catheter is inserted into the patient's body by a puncture through the patient's skin to position the end of the catheter at the infusion site. The needle is then retracted, from the catheter, with the catheter remaining in the vasculature and exiting the body through the skin.
A length of catheter (usually flexible tubing) external to the body is then looped and taped to the patient's skin under a bandage. This warm environment is conducive to evaporation of fluid on the outside of the exterior segment of the catheter and it has been found that this evaporation tends to draw fluid from the inside of the catheter.
Apparently, this withdrawal of fluid is due to the fact that the materials of which conventional catheters are made, e.g. implant grade polyurethane or silicone, have high water vapor transmission rates. When evaporation occurs as aforesaid, transpiration occurs and water moves through the tubing wall of the external catheter segment to the relatively dry external environment. This phenomenon draws fluid up the catheter and simultaneously allows blood from inside the patient's body to move up the catheter. After a period of time, the catheter tip usually occludes due to a thrombus formation. This blockage necessitates removal and replacement of the catheter thereby increasing the patient's risk of infection. According to standard practice, venous catheters are normally flushed daily with a solution of sodium heparin or saline to maintain patency (prevent thrombus formation).